man-pages/man4/sd.4

.\" sd.4
.\" Copyright 1992 Rickard E. Faith (faith@cs.unc.edu)
.\"
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.TH SD 4 1992-12-17 "" "Linux Programmer's Manual"
.SH NAME
sd \- Driver for SCSI Disk Drives
.SH SYNOPSIS
#include <linux/hdreg.h>        /* for HDIO_GETGEO */
#include <linux/fs.h>           /* for BLKGETSIZE and BLKRRPART */
.SH CONFIG
The block device name has the following form:
.BI sd lp,
where
.I l
is a letter denoting the physical drive, and
.I p
is a number denoting the partition on that physical drive.  Often, the
partition number,
.IR p ,
will be left off when the device corresponds to the whole drive.

SCSI disks have a major device number of 8, and a minor device number of
the form (16 *
.IR drive_number ") + " partition_number ,
where
.I drive_number
is the number of the physical drive in order of detection, and
.I partition_number
is as follows:
.sp
partition 0 is the whole drive
.br
partitions 1-4 are the DOS "primary" partitions
.br
partitions 5-8 are the DOS "extended" (or "logical") partitions

For example,
.I /dev/sda
will have major 8, minor 0, and will refer to all of the first SCSI drive
in the system; and
.I /dev/sdb3
will have major 8, minor 19, and will refer to the third DOS "primary"
partition on the second SCSI drive in the system.

At this time, only block devices are provided.  Raw devices have not yet
been implemented.
.SH DESCRIPTION
The following
.IR ioctl s
are provided:
.TP
HDIO_GETGEO
.RS
Returns the BIOS disk parameters in the following structure:
.RS
.nf
.ft B
struct hd_geometry {
      unsigned char heads;
      unsigned char sectors;
      unsigned short cylinders;
      unsigned long start;
};
.ft R
.fi
.RE

A pointer to this structure is passed as the
.BR ioctl (2)
parameter.

The information returned in the parameter is the disk geometry of the drive
.I "as understood by DOS!"
This geometry is
.I not
the physical geometry of the drive.  It is used when constructing the
drive's partition table, however, and is needed for convenient operation
of
.BR fdisk (1),
.BR efdisk (1),
and
.BR lilo (1).
If the geometry information is not available, zero will be returned for all
of the parameters.
.RE
.TP
BLKGETSIZE
Returns the device size in sectors.  The
.BR ioctl (2)
parameter should be a pointer to a
.BR long .
.TP
BLKRRPART
Forces a re-read of the SCSI disk partition tables.  No parameter is needed.

The
.BR scsi (4)
.IR ioctl s
are also supported.  If the
.BR ioctl (2)
parameter is required, and it is NULL, then
.BR ioctl ()
will return \-EINVAL.
.SH FILES
/dev/sd[a\-h]: the whole device
.br
/dev/sd[a\-h][0\-8]: individual block partitions
.\".SH "SEE ALSO"
.\".BR scsi (4)